This invention relates to a method of producing a bio-electrode which is used in a measurement for obtaining an electrocardiograph or the like and applied to the skin.
A conventional bio-electrode of such a kind is produced as shown in FIG. 2. In FIG. 2, a label 2 is stuck on one surface of a flat foam tape 1. Then, paint 5 of Ag or AgCl powder in which an ABS resin is used as a binder is applied to the surface which is in the side opposite to a projection 4a of an electrode element 4. A small hole 3 is formed at the center portion of the label 2, and the projection 4a of the electrode element 4 is inserted into the small hole 3 so that the electrode element 4 is attached to the label 2. Thereafter, sponge 6 is inserted into the foam tape 1, a catalyst such as boric acid or a borate solution is injected into the sponge 6, and a monomer such as a polyvinyl alcohol solution is then injected into the sponge. As a result of these procedures, the existence of the catalyst causes the hardness of the monomer to gradually increase so that a state where the sponge 6 is impregnated with solid gel is obtained. Finally, the sponge 6 is covered by a plastic cover 7. Instead of impregnating the sponge 6 with solid gel, the sponge 6 may be impregnated with paste.
Since paste is not used in sponge impregnated with solid gel, the sponge is not sticky. After the sponge is peeled from a skin, therefore, it is not required to wipe off a sticky substance. However, the nonuse of paste and the low water content of the sponge cause a problem to arise that the electric skin resistance is so high that it requires a long period to drop to a low level. This causes a drift or a polarization voltage to be generated until the electric skin resistance becomes stable in level, whereby the measurement may be adversely affected.
By contrast, in sponge impregnated with the paste, the use of paste makes the electric skin resistance low and hence the electric skin resistance drops to a low level in a short period. This allows the measurement to be stably performed immediately after the application of a bio-electrode. When the cover 7 is pressed during storage of a bio-electrode, however, paste oozes out from the adhesive interface between the foam tape and the cover so that the surroundings are stained with the paste.